This invention relates generally to display technologies and more particularly concerns a display which produces a specified set of images wherein each image is displayed with high resolution and can be arbitrarily complex, yet only requires a minimal number of drivers.
A wide variety of display technologies exist including LEDs, LCDs, CRT""s, electrophoretic and gyricon technologies. What each of these displays has in common is that they must all be addressed. Three of the most common types of addressing schemes for displays are active matrix addressing, passive matrix address and stylus or wand addressing.
Active matrix addressing places the least demands on the properties of the display because a separate addressing electrode is provided for each pixel of the display and each of these electrodes is continuously supplied with an addressing voltage. The complete set of voltages can be changed for each addressing frame. While this type of addressing places the least demands on the properties of the display medium, active matrix addressing is the most expensive, most complicated and least energy efficient type of addressing.
Passive matrix addressing makes use of two sets of electrodes, one on each side of the display medium. Typically, one of these consists of horizontal conductive bars and the other consists of vertical conductive bars. The bars on the front surface or window of the display are necessarily transparent. To address the display medium, a voltage is placed on a horizontal conductive bar and a voltage is placed on a vertical conductive bar. The segment of medium located at the intersection of these two bars experiences a voltage equal to the sum of these two voltages. If the voltages are equal, as they usually are, the sections of medium located adjacent to the each of the bars, but not at the intersection of the bars, experience xc2xd the voltage experienced by the section of medium at the bar intersection. Passive addressing is less complicated and more energy efficient because the pixels of the display medium are addressed only for as long as is required to change their optical states. However, the requirements for a medium that can be addressed with a passive matrix display are significantly greater than for the active matrix case. The medium must respond fully to the full addressing voltage but it must not respond to xc2xd the full addressing voltage. This is called a threshold response behavior. The medium must also stay in whichever optical state it has been switched into by the addressing electrodes without the continuous application of voltage, that is it should store the image without power. Passive addressing is the most widely used method of addressing displays and is the lowest cost.
Stylus or wand addressing consists of either an addressing electrode or an array of addressing electrodes that can be moved over the surface of the display medium. Typically, the medium is placed over a grounding electrode and is protected from possible mechanical damage from the stylus or wand by placing a thin window between the stylus or wand and the display. As the stylus or wand is moved over the display medium, it applies voltages to specific pixels of the medium for short periods of time and generates a full image each time the stylus or wand is scanned over the surface. In a variation on this method, the wand may comprise a two dimensional array of electrodes that is placed in contact with the surface of the display medium.
In each of these cases, the smallest size addressing unit, called a pixel is addressed. Each pixel has the same area and shape as neighboring pixels, only its location differs from the other pixels on the display. As the pixel size decreases the resolution of the displayed image increases but so also does the complexity of the addressing device and the number of drivers needed to address the display medium, because the number of driver circuits that are required is proportional to the square of the resolution. For example, an active matrix display with a 100 pixels/inch resolution that is 10 inches by 10 inches would require 1,000,000 drivers or one driver for each pixel. The same display configured with for a passive matrix addressing system would require 2,000 drivers, or one driver for each row and one driver for each column.
As the complexity of the addressing device rises, so also does the cost. Therefore, there is always a tension between displaying the best possible image with the highest resolution and using the least complex and most cost effective means of addressing the display.
The alternative to pixel addressing has been to fabricate addressing electrodes with fixed images such as are used in pagers, watches, cellular phones and clock radios etc. This allows for good resolution of a specific limited set of images cheaply. The drawback however, is that only a single fixed image can be produced in a specific location on a display. Taking as an example, the display for a clock, portions of the display may be reserved to display the time, a pm indicator, an alarm indicator, a xe2x80x9csnoozexe2x80x9d indicator, and a low battery indicator. Time may be displayed using the typical 8-segment numerical display in which 8 fixed displayable segments have been chosen which can be combined to form the various numbers. Time will always be displayed in the same portion of the display, as will the other indicators that are displayed on the clock face. For instance, the low battery indicator may consist of a small icon shaped like a broken battery which blinks in one comer of the display. The low battery icon could never, for instance, alternate with the time in the same portion of the display. Therefore, the entire display consists of independent, separately addressable, non-overlapping fixed images which can either be selected or not. This reduces the complexity of the addressing device and limits the number of drivers needed to the number of images displayed.
Up to this point, the choice of addressing displays has therefore been limited to higher complexity and cost pixel addressing which allows for the unlimited choice of images which can be displayed in any region of the display, or low complexity and cost addressing which uses reserved areas to display a single fixed image. However, there exists a need for displays which are capable of showing a limited set of fixed images which are not relegated to specific portions of the display and which use a low complexity/cost addressing system.
To use the clock example again, it might be useful to have the low battery image alternate with the time in the same portion of the display to provide a more readily noticeable indication that the battery is low. Another example is a highway sign which could be used to display varying road and weather conditions such as ice, rain, snow, and fog ahead. Further examples include point of sale advertising signage which might display the various products for sale by a vendor in a freezer case.
Accordingly, it is the primary aim of the invention to provide a display capable of displaying, at high resolution, a set of known, overlapping, arbitrarily complex fixed images without requiring a correspondingly complex addressing system requiring a large number of addressing drivers.
By precomputing all of the intersections of these images, the number of drivers that are required becomes a function of the number of images rather than a function of the resolution. For example, four arbitrarily complex, overlapping images require, at most, 16 drivers. In general, n arbitrarily complex, overlapping images require, at most, 2n drivers. This result holds irrespective of the size of the display, the complexity of the images, resolution, or amount of overlap of the images.
It is possible to further reduce the number of drivers if some of the images do not overlap some of the other images. For example, consider the case where two images overlap each other in one area and two other images overlap each other in a separate area. However, the two sets of images do not overlap. In this case, at most eight drivers are needed instead of the 16 drivers that would be required if all four of the images overlapped each other. In general, if you consider N separate, distinct areas, each with a set of overlapping images where ni images overlap in area i (ie, n1 images that overlap in area 1, n2 images that overlap in area 2, etc.). Then the maximum number of drivers that are required will be summation for I from 1 to N of 2 raised to the power of ni.
This invention discloses a method to greatly simplify and reduce the cost of displays when all of the images that need to be displayed are known beforehand. Applications include (but are not limited to) road signs, informational signs, advertising, user interfaces to electronic equipment, and many other applications.
Further advantages of the invention will become apparent as the following description proceeds.
Briefly stated and in accordance with the present invention, there is provided an addressing system for producing a set of N overlapping images, each image having at least an image portion, on at least a portion of a display medium which uses no more than 2N drivers in combination with a plurality of electrodes responsive to the drivers such that said plurality of electrodes can cause the display medium to display any one of the N images.
There is also provided a means of reducing the number of drivers needed to display a set of N overlapping images, each image having at least an image portion, on at least a portion of a display medium by using a plurality of electrodes, each electrode having a usage vector and electrically connecting together at least 2 electrodes having identical usage vectors.
Further, there is also provided a display for producing a set of N overlapping images, each image having at least an image portion, on at least a portion of a viewing surface of the display using a display medium, no more than 2N drivers, and a plurality of electrodes responsive to said plurality of drivers such that said plurality of electrodes can cause the display medium to display any one of the N images.
There is also provided a display which uses a reduced number of drivers needed to display a set of N overlapping images on a viewing surface of a display, each image having at least an image portion, on at least a portion of a display medium by using a plurality of electrodes, each electrode having a usage vector and electrically connecting together at least 2 electrodes having identical usage vectors.